This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol1", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
2. The effects upon the system, or on parts more or less remote from the surface of application, are next to be considered. These depend upon the absorption of the iron, and are usually not exhibited until a considerable time after its introduction into the stomach. That iron is absorbed has been proved by numerous experiments. Tiedemann and Gmelin found it in the serum of the blood of the mesenteric and portal veins of a horse, to which they had six hours previously given a solution of the sulphate. M. Quevenne has shown that, if iron passes with the urine at all in the normal state, it is in extremely small proportion'; and that, after the use of the ferruginous preparations for a short time, the quantity, though still very small, is appreciably increased; proving that, while the kidneys are not the avenue by which the metal is mainly eliminated from the system, it must have been absorbed in order to produce the slight increase observed. (Archives de Physiol., Oct. 1854, p. 104.) It is said also to have been found in the milk, perspiration, and bile. In what state it enters the blood is uncertain; but it is highly probable that, in part at least, it does so, as before stated, in union with an organic principle, and that, in this condition, it contributes directly to the construction of the red corpuscles. Another portion may circulate in the serum in other soluble forms, and simply act as a tonic and perhaps astringent upon the tissues.
After iron has been taken in the ordinary medicinal doses for a few days, often in less than a week, its effects on the system may be seen in an increased redness of the complexion, the lips, and the tongue, a fuller and stronger pulse, and a general exaltation of the organic functions. These results proceed from a greater richness of the blood, in which the proportion of the red corpuscles is increased. If the use of the medicine be continued, a plethoric condition may be induced, indicated by fulness or dull pains in the head, sluggishness of mind, a full strong pulse, increased heat, and a heightened colour of the surface. It is said that pustules of acne are apt to appear on the face, breast, and back. This is a morbid condition, predisposing to active congestion, hemorrhage, and probably inflammation. Hence the danger of an excessive and long-continued use of the natural chalybeate waters, against which they who frequent watering places should be placed upon their guard. These effects are scarcely sufficient to rank iron among medicines poisonous to the constitution. They are but an exaltation of the healthy powers and functions, such as may result from an abuse of food and other agents essential to life. The only mode in which any preparation of iron can become poisonous, is, as before mentioned, by irritating and inflaming the stomach and bowels.
Iron has been immemorially employed in medicine. It has two modes of therapeutic action; one, by a gentle excitement of the functions, and a somewhat constricting effect on the tissues, evinced in the surfaces to which it is directly applied, whether external or internal, and in distant organs or the system generally, through which it circulates in the serum of the blood; and the other, as a reconstructive agent, by affording the material and the influence necessary for the production of new blood-corpuscles, to supply the place of those which may have been lost. In the first method, it operates as ordinary tonics possessing some astringent power; in the second, its influence is quite peculiar and characteristic, unless, as some assert, it may be imitated by manganese. Some therapeutists believe that this reconstructive operation is essentially and purely tonic; that is, that the iron taken as a medicine acts simply by a gentle exaltation of all the blood-making functions, enabling them to form the red corpuscles more abundantly, not by furnishing the material, but by increasing their power of assimilating nutriment. Others, again, think that it acts simply by furnishing an essential constituent of the corpuscles, and that in fact it is nothing more than an article of food. It is probable that the truth embraces both these opinions; and that the chalybeates, in augmenting the red corpuscles, really stimulate the functions, while they render the material more accessible, and furnish it in a state more readily acted on, than as it exists in the ordinary diet. In referring to the several diseases in which iron is used, I shall endeavour to keep in view the two methods of operating here described, though they are often conjoined in the same disease.
1. As a mere tonic, iron is much and very advantageously used in debility of the digestive organs. Connected with laxatives and aroma-tics, it is among the most useful remedies in dyspepsia, and its assodated and dependent affections. When no effect on the system at large is required, and the indication is simply to stimulate the mucous membrane of the primae viae, one of the soluble preparations should be preferably selected. Unless the medicine is given too largely, the tendency is to produce constipation; and hence the propriety of administer- ' ing laxatives at the same time. Should irritation of stomach or bowels be induced, the inference is that too much has been given, and the dose should be diminished within the irritating point. Not unfrequently, in these cases, the chalybeate is associated with one of the simple bitters, as well as with a laxative and aromatic; and these may be combined, in the form of pill, powder, infusion, or tincture, to suit the particular necessities of the case.
The astringency of the preparations of iron renders them, in connection with their tonic property, advantageous also in chronic diarrhoea attended with relaxation of the mucous tissue. The saline preparation-are preferred for this purpose, especially the sulphate, and the solution of the nitrate, the latter of which was introduced into use chiefly for its supposed efficacy in this complaint. Great care should be taken not to give them in irritating doses; and they may often be usefully associated with an opiate.